Offshore fluid transfer system

ABSTRACT

Apparatus ( 12 ) for transferring fluid between floating vessels ( 10, 11 ) is described, comprising a submerged rigid transfer arm ( 13 ) carrying a fluid pipeline ( 16 ). The apparatus ( 12 ) is provided with thrusters ( 21 ) and positioning monitoring means ( 24 ). A control system ( 25 ) operates the thrusters ( 21 ) to move the arm ( 13 ) if the position monitoring means ( 24 ) shows the arm ( 13 ) and the second vessel ( 11 ) is outside a given range, to restore the separation to within the range. The pipeline ( 16 ) may be located in a tunnel ( 30 ) on the arm ( 13 ) which opens above the waterline at each end to allow personnel access therein for inspection and maintenance of the pipeline ( 16 ).

The present invention relates to apparatus for transferring fluidbetween two structures, for example two floating vessels, or a fixedoffshore structure and a vessel.

Transferring fluid, particularly of a cryogenic product, between twofloating vessels, or a fixed offshore structure and a vessel, is adifficult and hazardous operation when performed in open sea. Varioussystems for transferring fluid have been proposed. For example, UKpatent 2328196 describes a system which employs a rigid arm, one end ofwhich is fixed in an articulated fashion to a storage vessel. The otherend is supported by means of a flotation tank. A receiving vessel can bemoored to this end of the rigid arm to receive fluid transferred fromthe storage vessel. The fluid transfer system between the rigid arm andthe receiving vessel may be handled by articulated rigid pipes, forexample of the type described in U.S. Pat. No. 3,556,148.

One disadvantage of such a system is that when the rigid arm isconnected to the floating vessel, the action of wind and waves may causesudden changes in the separation of the arm and vessel. This may imposeunacceptable loads on the fluid transfer system or even cause the armand vessel to collide. Therefore, there is a need to improve therelative motion behaviour between the rigid arm and the recipientvessel.

A further disadvantage is that because the rigid arm is submerged,inspection, maintenance and repair operation are more difficult to carryout.

Accordingly, in a first aspect, the present invention provides apparatusfor transferring fluid between a first structure and a floating vessel,comprising a rigid transfer arm carrying a fluid pipeline for receivingfluid from a first structure, means to attach a first end of the arm tothe first structure so as to allow the arm to pivot about at least twoaxes, loading means located at the second end of the arm and attachableto a floating vessel for transferring fluid from the fluid pipeline tothe floating vessel, wherein the apparatus is provided with thrust meansoperable to rotate the rigid arm relative to the first structure about asubstantially vertical axis in use, position monitoring means to monitorthe separation of a point on the arm and the floating vessel and acontrol system operable to actuate the thrust means if the separation isoutside a predetermined range, so as to move the arm relative to thefloating vessel thereby to restore the separation to within thepredetermined range.

In a second aspect, the invention provides apparatus for transferringfluid between first and second floating vessels, comprising a submergedrigid transfer arm, at least one fluid pipeline for transferring fluidbetween the first and second vessels, the pipeline located in a conduitwhich is mounted on the arm and which has an opening at each end whichis above the water line in use, means to attach a first end of the armto the first vessel at a position above the water line in use so as toallow the arm to pivot about three axes, loading means located at thesecond end of the arm and attachable to the second vessel fortransferring fluid from the fluid pipeline to the second vessel.

This allows easier access to the attachment means and pipeline forinspection and maintenance.

In this way, the risk of large loads or collisions damaging the transfersystem is reduced.

The first structure may itself be another floating vessel or a seabedmounted structure.

The rigid arm may be a space frame construction having a plurality oflongitudinal members joined by a plurality of transverse bracingmembers. In one embodiment, the fluid pipeline is located inside aconduit formed at least in part by one of the longitudinal members.Insulation may be provided around the fluid pipeline.

Advantageously, the conduit is configured to allow access thereinto forinspection and maintenance of the fluid pipeline.

Preferably, apparatus in accordance with the second aspect of theinvention is also provided with thrust means operable to rotate therigid arm relative to the first vessel about a substantially verticalaxis in use, position monitoring means to monitor the separation of apoint on the arm and the second vessel, and a control system operable toactuate the thrust means if the separation is outside a predeterminedrange, so as to move the arm relative to the second vessel thereby torestore the separation to within the predetermined range.

The apparatus may usefully comprise mooring means to moor the apparatusto the floating vessel, means to monitor whether the mooring means isattached to the floating vessel and means to automatically disconnectthe loading device from the floating vessel if the mooring means becomesdetached from the floating vessel.

Similarly, the apparatus may also include mooring means to moor thefloating vessel to the structure, means to monitor whether the mooringmeans is attached to the floating vessel and means to automaticallydisconnect the loading device from the floating vessel if the mooringmeans becomes detached from the floating vessel.

In these cases, if the loading device is automatically disconnected fromthe floating vessel, the control means is preferably operable to actuatethe thrust means to move the arm away from the floating vessel.

Preferably, the fluid pipeline is provided with flexible connectionsallowing it to bridge the pivot points in the apparatus.

In a preferred embodiment, the loading means comprises a cryogenicloading device.

Typically, the apparatus further comprises float means at the second endof the arm, comprising at least one buoyancy device extending both aboveand below the water line in use.

The float means may comprise two mutually spaced buoyancy devices, eachof which extends both above and below the water line in use.

Alternatively, the float means may comprise two mutually spacedsubmerged buoyancy devices which are connected to each other at,theirupper ends and single buoyancy device extending above the water line inuse.

In the second aspect of the invention, the rigid arm is typically aspace frame construction having a plurality of longitudinal membersjoined by a plurality of transverse bracing members, forming aperipheral frame within which the conduit is located.

Advantageously, a fender system is provided at the second end of therigid arm.

In use, the submerged rigid arm will generally be substantiallyhorizontal.

The invention also provides a method of transferring fluid from a firststructure to a floating vessel using the apparatus as described above,comprising the steps of: actuating the thrust means to pivot the arm ina first direction about an axis defined by the attachment means relativeto the first structure, moving the floating vessel into a position inthe vicinity of the first structure, actuating the thrust means to pivotthe arm in a second direction opposite to the first direction so as tobring the loading means adjacent the floating vessel, connecting theloading means to the vessel and transferring fluid from the fluidconduit to the floating vessel, disconnecting the loading means from thefloating vessel, and actuating the thrust means to pivot the arm in thefirst direction away from the floating vessel; wherein, while theloading device is connected to the floating vessel, monitoring theseparation between a point on the arm and the vessel, and operating thethrust means if the separation is outside a predetermined range so as tomove the arm relative to the vessel, thereby to restore the separationto within the predetermined range.

The method may further comprise the step of monitoring whether mooringmeans on the arm is attached to the floating vessel and in the event ofdetachment, automatically disconnecting the loading device from thefloating vessel.

The method may further comprise the step of monitoring whether mooringmeans on the structure is attached to the floating vessel and in theevent of detachment, automatically disconnecting the loading device fromthe floating vessel.

In the event of automatic disconnection of the loading device from thefloating vessel, the thrust means is preferably operated to move the armin the first direction away from the floating vessel.

The invention will now be described in detail, by way of example ofonly, with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of an apparatus for transferring fluidbetween two floating vessels in accordance with a first embodiment ofthe invention;

FIG. 2 is a cross section of the rigid arm shown in FIG. 1 along theline A-A;

FIG. 3 shows the apparatus of FIG. 1 from above (in solid lines) andwhen not in use (in dotted lines);

FIG. 4 is a schematic diagram of an apparatus for transferring fluidbetween a seabed pipeline and a vessel in accordance with a secondembodiment of the invention;

FIG. 5 is a schematic diagram of an apparatus for transferring fluidbetween two floating vessels in accordance with a third embodiment ofthe invention;

FIG. 6 is a cross section of the rigid arm shown in FIG. 5 along theline A-A;

FIGS. 7 and 8 are schematic diagrams of two embodiments of the floatmeans at the distal end of the transfer apparatus.

Referring now to FIG. 1, a first floating vessel 10 is shown, which maybe a production or storage vessel moored to the seabed by anyconventional and appropriate means. A second floating vessel 11, whichmay be a shuttle tanker for transporting fluid such as liquid naturalgas away from the production/storage vessel 10, is located nearby. Thetransfer apparatus 12 is shown in use, connecting the two vessels 10,11.

The transfer apparatus 12 consists of a submerged rigid arm 13,typically of space frame type construction. As shown in FIG. 2, the arm13 may be formed of three longitudinal members 14 arranged in atriangular form and joined by a number of transverse bracing members 15.

Piping 16, for example rigid steel piping, is attached to the arm andcarries the fluid being transferred. The piping 16 may be located insideone or more of the longitudinal members 14 and insulation (not shown)may also be provided. This construction protects the piping 16 but alsoallows the possibility of inspection of the piping 16.

At a first, proximal end of the arm 13, attachment means 17 is providedfor attaching the arm 13 to the first vessel 10, preferably at thestern. The attachment means 17 may be constructed in any convenient formwhich includes articulations allowing the arm 13 to pivot about at leasttwo axes relative to the vessel 10, preferably the vertical axis 18 andthe horizontal axis extending perpendicularly into and out of the planeof the paper. The attachment means 17 projects downwardly from thevessel 10 and is dimensioned such that the arm 13 is located underwaterat a depth greater than the maximum draught of both the first and secondvessels 10, 11.

At the second, distal end of the arm 13, float means 19 is providedwhich extends upwardly from the arm 13 and projects above the watersurface.

A loading device 20, which is preferably a cryogenic loading device ofknown form, is located on the top of the float means 19. Articulationsmay be provided to allow the loading device 20 to pivot relative to thefloat means 19. The loading device 20 is connected to the piping 16 andis connectable to the second vessel 11 to allow transfer of fluid fromthe piping 16 to the vessel 11. Preferably the loading device 20 isconfigured to allow fluid pumped from the first vessel 10 to be readilyreturned to it, for example in the case of an emergency disconnect fromthe second vessel 11.

The piping 16 is preferably provided with flexible connections such asswivel joints or flexible hoses where necessary to allow it to bridgethe various points of articulation in the apparatus 12.

The rigid arm 13 is preferably designed to be of a suitable length suchthat in use, when the proximal end is attached to the stern of the firstvessel 10, its distal end will be adjacent a midship portion of thesecond vessel 11.

At the lower end of the float member 19, one or more thrusters 21 islocated. The or each thruster 21 is powered and controlled from thefirst vessel 10, for the purpose described further below.

When transfer of fluid to a second vessel 11 is required, the thrusters21 are used to rotate the arm 13 about the vertical axis 18, for exampleto rotate it anti-clockwise if viewed from above in FIG. 1, so that itdoes not obstruct the area around the stern of the first vessel 10. Thesecond vessel 11 can then be manoeuvred into position adjacent the firstvessel 10 as shown in FIG. 1. The first and second vessels 10, 11 maynow be moored stern to bow by a line 22, for example an elastic line, asshown in FIGS. 1 and 3.

Once the second vessel 11 is in position the thrusters 21 are operatedagain to rotate the arm 13 in the opposite direction, (clockwise whenviewed from above in FIG. 1) to bring the float means 19 and loadingdevice 20 adjacent preferably the midship portion of the second vessel11. The rigid arm 13 is moored to the vessel 11 by any suitable mooringmeans, such as mooring lines 23 shown schematically in FIG. 1. Theloading device 20 is connected to the appropriate fluid receivingapparatus on board the vessel 11 so that fluid from the piping 16 can betransferred to the second vessel 11. When transfer is complete, themooring means 23 is disconnected from the vessel 11. The thrusters 21are then operated to rotate the arm 13 away from the vessel 11, allowingit to leave the area unobstructed.

When the loading device 20 is moored to the vessel 11, the thrusters 21are also employed to maintain the rigid arm 13 in a substantially fixedposition relative to the vessel 11, to ensure that no unacceptable loadsare imposed on the loading device 20 and various interconnectionsbetween the piping 16 and the vessel 11.

A position monitoring device 24 is mounted on a point on the transferapparatus 12, for example on the float means 19, to monitor continuouslythe separation of that point from the hull of the vessel 11. Forexample, the position monitoring device 24 may act by electronic orvisual means. A control system 25 preferably located on the first vessel10 receives information from the position monitoring device 24. If thetransfer apparatus 12 and the vessel 11 move towards or away from oneanother so that their separation is no longer within an acceptablerange, the control system 25 responds by operating the thrusters 21 tomove the transfer apparatus 12 in an appropriate direction so as torestore the transfer apparatus 12 and the vessel 11 to within anacceptable separation range. In this way, any relative movement due tothe action of wind and waves can be accommodated to avoid the risk ofdamaging the transfer apparatus 12 and/or the vessel 11.

Preferably, the apparatus also comprises means 26 to monitor whether themooring means 23 is actually attached to the vessel 11 and/or whetherthe line 22 is attached to the vessel 11. If the mooring means 23 and/orline 22 become accidentally detached from the vessel 11, the controlsystem 25 operates to automatically disconnect the loading device 20from the vessel 11, to avoid any damage to the loading device 20 whichmight occur if the separation of the vessel 11 and the transferapparatus 12 changes significantly due to detachment of the mooringmeans 22, 23.

Furthermore, if the control system 25 operates in this way to disconnectthe loading device 20 from the vessel 11, it also operates the thrusters21 to move the rigid arm 13 well away from the vessel 11, to avoid thedanger of collision.

In this way, the safety of the transfer operation is improved and theservice life of the transfer apparatus 12 increased.

When the transfer apparatus 12 is not being used, it may have its distalend secured to the first vessel 10. For example, if the transferapparatus 12 is attached to the stern of the vessel 10, it can bepivoted back round so that its distal end can be secured to the vessel10 towards the bow region as shown in dotted lines in FIG. 3. In thisway the transfer apparatus 12 is able to withstand extreme weatherconditions which may exceed its design parameters. It also allowsinspection, repair and maintenance to be carried out more easily.

Although the invention has been described with reference to transferringfluid between two floating vessels it will be appreciated that it isalso applicable to transfer between a fixed structure and a vessel.

For example, as shown in FIG. 4 the fixed structure may comprise a base27 mounted on the seabed from which a column 28 rises to above thesurface of the water. The base 27 may be a well-head, or connected by aseabed pipeline to a well-head or onshore plant. The arm 13 is attachedto the column 28 by articulated attachment means 17 and the vessel 11may be moored to the column 28 by a line 22. The other features are thesame as in the first embodiment.

Another embodiment of transfer apparatus 12 is shown in FIG. 5 fortransfer between two floating vessels 10, 11. This is generally similarto the first embodiment of FIG. 1. However, in this case, at its first,proximal end the arm 13 includes an upward projection 13 a which extendsup above the waterline and is connected to the first vessel 10 byattachment means 17. The attachment means 17 may be constructed in anyconvenient form which includes articulations allowing the arm 13 topivot about three axes relative to the vessel 10, preferably thevertical axis 18, a horizontal axis extending into and out of the planeof the paper and a horizontal axis parallel with the plane of the paper.

The upward projection 13 a and the attachment means 17 are sized suchthat the horizontal portion of the arm 13 is located underwater at adepth greater than the maximum draught of both the first and secondvessels 10, 11. This construction allows easier access to the attachmentmeans 17 for inspection, maintenance and repair.

In this embodiment, the float means 19 at the distal end of the arm 13preferably incorporates at least one and preferably two buoyancy devices31, 32 as shown in FIG. 7. In this example, the buoyancy devices 31, 32are substantially cylindrical members which are mutually spaced andproject both above and below the waterline. Alternatively, as shown inFIG. 8, there may be two mutually spaced buoyancy devices 33, 34 belowthe waterline which are joined at their upper ends to create a singlebuoyancy device 35 which projects up above the waterline. Since theattachment means 17 provides 3 degrees of freedom for the transferapparatus 12, these configurations of buoyancy devices provide theentire assembly with a natural stability. It will be appreciated thatbuoyancy means as shown in FIGS. 7 and 8 could also be used in theembodiments of FIGS. 1 and 4.

Another feature of the third embodiment is that the piping 16 is locatedinside a conduit or tunnel 30 which extends the length of the arm 13,for example within the space frame construction, as seen in FIG. 6. Thetunnel 30 has an opening above the waterline at the proximal end of thetransfer apparatus 12 and extends continuously to another opening abovethe waterline at the distal end. The tunnel 30 and openings are designedto permit personnel entry and movement therealong. In this way theentire length of pipeline 16 is accessible in a substantially dryenvironment for inspection, repair and maintenance, avoiding the needfor divers.

It will be appreciated that the feature of the upward projection 13 aand location of the attachment means 17 above the waterline, and thefeature of the tunnel 30 could also be used in the first and secondembodiments of transfer apparatus described above.

As in the other embodiments, the piping 16 is preferably provided withflexible connections such as swivel joints or flexible hoses wherenecessary to allow it to bridge the various points of articulation inthe apparatus 12.

It will be appreciated that the invention provides an improved fluidtransfer system for use in an offshore environment and that othermodifications and variations to the specific embodiments described arealso possible.

1. Apparatus for transferring fluid between a first structure and afloating vessel, comprising: a submerged rigid transfer arm carrying afluid pipeline for receiving fluid from a first structure, means toattach a first end of the arm to the first structure so as to allow thearm to pivot about at least two axes, loading means located at thesecond end of the arm and attachable to a floating vessel fortransferring fluid from the fluid pipeline to the floating vessel,wherein the apparatus is provided with thrust means operable to rotatethe rigid arm relative to the first structure about a substantiallyvertical axis in use, position monitoring means to monitor theseparation of a point on the arm and the floating vessel and a controlsystem operable to actuate the thrust means if the separation is outsidea predetermined range, so as to move the arm relative to the floatingvessel thereby to restore the separation to within the predeterminedrange.
 2. Apparatus for transferring fluid between first and secondfloating vessels, comprising: a submerged rigid transfer arm, at leastone fluid pipeline for transferring fluid between the first and secondvessels, the pipeline located in a conduit mounted on the arm and havingan opening at each end which is above the waterline, means to attach afirst end of the arm to the first vessel at a position above the waterline in use so as to allow the arm to pivot about three axes, loadingmeans located at the second end of the arm and attachable to the secondvessel for transferring fluid from the fluid pipeline to the secondvessel.
 3. Apparatus as claimed in claim 1, wherein the first structureis a floating vessel.
 4. Apparatus as claimed in claim 1, wherein thefirst structure is a seabed mounted structure.
 5. Apparatus as claimedin claim 1, wherein the rigid arm is a space frame construction having aplurality of longitudinal members joined by a plurality of transversebracing members.
 6. Apparatus as claimed in claim 1, wherein the fluidpipeline is located inside a conduit formed at least in part by one ofthe longitudinal members.
 7. Apparatus as claimed in claim 6, whereininsulation is provided around the fluid pipeline.
 8. Apparatus asclaimed in claim 2, wherein the fluid pipeline is provided with flexibleconnections allowing it to bridge the pivot points in the apparatus. 9.Apparatus as claimed in claim 2, wherein the apparatus is provided withthrust means operable to rotate the rigid arm relative to the firstvessel about a substantially vertical axis in use, position monitoringmeans to monitor the separation of a point on the arm and the secondvessel, and a control system operable to actuate the thrust means if theseparation is outside a predetermined range, so as to move the armrelative to the second vessel thereby to restore the separation towithin the predetermined range.
 10. Apparatus as claimed in claim 1,further comprising mooring means to moor the apparatus to the floatingvessel, means to monitor whether the mooring means is attached to thefloating vessel and means to automatically disconnect the loading devicefrom the floating vessel if the mooring means becomes detached from thefloating vessel.
 11. Apparatus as claimed in claim 1, further comprisingmooring means to moor the floating vessel to the first structure, meansto monitor whether the mooring means is attached to the floating vesseland means to automatically disconnect the loading device from thefloating vessel if the mooring means becomes detached from the floatingvessel.
 12. Apparatus as claimed in claim 10, wherein if the loadingdevice is automatically disconnected from the floating vessel, thecontrol means is operable to actuate the thrust means to move the armaway from the floating vessel.
 13. Apparatus as claimed in claim 1,wherein the fluid pipeline is provided with flexible connectionsallowing it to bridge the pivot points in the apparatus.
 14. Apparatusas claimed in claim 1, wherein the loading means comprises a cryogenicloading device.
 15. Apparatus as claimed in claim 1, further comprisingfloat means at the second end of the arm, comprising at least onebuoyancy device extending both above and below the water line in use.16. Apparatus as claimed in claim 15, wherein the float means comprisestwo mutually spaced submerged buoyancy devices which are connected toeach other at their upper ends and single buoyancy device extendingabove the water line in use.
 17. Apparatus as claimed in claim 15,wherein the rigid arm is a space frame construction having a pluralityof longitudinal members joined by a plurality of transverse bracingmembers, forming a peripheral frame within which the conduit is located.18. Apparatus as claimed in claim 7, wherein the rigid arm is a spaceframe construction having a plurality of longitudinal members joined bya plurality of transverse bracing members, forming a peripheral framewithin which the conduit is located.
 19. Apparatus as claimed in claim1, further comprising a fender system at the second end of the rigidarm.
 20. Apparatus as claimed in claim 1, wherein, in use the submergedrigid arm is substantially horizontal.
 21. A method of transferringfluid from a first structure to a floating vessel using the apparatus asclaimed in any preceding claim, comprising the steps of: actuating thethrust means to pivot the arm in a first direction about an axis definedby the attachment means relative to the first structure, moving thefloating vessel into a position in the vicinity of the first structure,actuating the thrust means to pivot the arm in a second directionopposite to the first direction so as to bring the loading meansadjacent the floating vessel, connecting the loading means to the vesseland transferring fluid from the fluid conduit to the floating vessel,disconnecting the loading means from the floating vessel, and actuatingthe thrust means to pivot the arm in the first direction away from thefloating vessel; further comprising, while the loading device isconnected to the floating vessel, monitoring the separation between apoint on the arm and the vessel, and operating the thrust means if theseparation is outside a predetermined range so as to move the armrelative to the vessel, thereby to restore the separation to within thepredetermined range.
 22. A method as claimed in claim 21, furthercomprising the step of monitoring whether mooring means on the arm isattached to the floating vessel and in the event of detachment,automatically disconnecting the loading device from the floating vessel.23. A method as claimed in claim 21, further comprising the step ofmonitoring whether mooring means on the structure is attached to thefloating vessel and in the event of detachment, automaticallydisconnecting the loading device from the floating vessel.
 24. A methodas claimed in claim 22, wherein the event of automatic disconnection ofthe loading device from the floating vessel, the thrust means isoperated to move the arm in the first direction away from the floatingvessel.
 25. Apparatus as claimed in claim 2, wherein the first structureis a floating vessel.
 26. Apparatus as claimed in claim 2, wherein thefirst structure is a seabed mounted structure.
 27. Apparatus as claimedin claim 2, wherein the rigid arm is a space frame construction having aplurality of longitudinal members joined by a plurality of transversebracing members.
 28. Apparatus as claimed in claim 2, wherein the fluidpipeline is located inside a conduit formed at least in part by one ofthe longitudinal members.
 29. Apparatus as claimed in claim 2, furthercomprising mooring means to moor the apparatus to the floating vessel,means to monitor whether the mooring means is attached to the floatingvessel and means to automatically disconnect the loading device from thefloating vessel if the mooring means becomes detached from the floatingvessel.
 30. Apparatus as claimed in claim 2, further comprising mooringmeans to moor the floating vessel to the first structure, means tomonitor whether the mooring means is attached to the floating vessel andmeans to automatically disconnect the loading device from the floatingvessel if the mooring means becomes detached from the floating vessel.31. Apparatus as claimed in claim 2, wherein the fluid pipeline isprovided with flexible connections allowing it to bridge the pivotpoints in the apparatus.
 32. Apparatus as claimed in claim 2, whereinthe loading means comprises a cryogenic loading device.
 33. Apparatus asclaimed in claim 2, further comprising float means at the second end ofthe arm, comprising at least one buoyancy device extending both aboveand below the water line in use.
 34. Apparatus as claimed in claim 2,further comprising a fender system at the second end of the rigid arm.35. Apparatus as claimed in claim 2, wherein in use the submerged rigidarm is substantially horizontal.
 36. Apparatus as claimed in claim 28,wherein insulation is provided around the fluid pipeline.
 37. Apparatusas claimed in claim 29, wherein if the loading device is automaticallydisconnected from the floating vessel, the control means is operable toactuate the thrust means to move the arm away from the floating vessel.38. Apparatus as claimed in claim 33, wherein the float means comprisestwo mutually spaced buoyancy devices, each of which extends both aboveand below the water line in use.
 39. Apparatus as claimed in claim 33,wherein the float means comprises two mutually spaced submerged buoyancydevices which are connected to each other at their upper ends and singlebuoyancy device extending above the water line in use.
 40. Apparatus asclaimed in claim 36, wherein the rigid arm is a space frame constructionhaving a plurality of longitudinal members joined by a plurality oftransverse bracing members, forming a peripheral frame within which theconduit is located.